Diagnosis: Locomotive form semicircular or fan-shaped, often with long ‘tail’. Frontal hyaloplasm occupies about half of the cell; the front edge may be smooth or slightly wavy. Rapidly moving cells often have a long ‘tail’; in cultures and moist-chamber-preparations amoebae are commonly covered with patches of fecal pellets. Locomotive forms vary in size. Rounded vesicular nucleus 6—11 um in diameter with single spherical central nucleolus. Floating form of radial type, with a number of fine, tapering hyaline pseudopodia. Ultrastructure: Cell surface is covered with glycostyles about 100 nm in length; simple, filaments present among them.